1. Field of the Invention
The present invention relates to a plasma processing apparatus and a plasma processing method for plasma processing a workpiece by generating plasma. More specifically, the present invention relates to how a processing gas to be used to generate plasma may be supplied.
2. Description of the Related Art
There are plasma processing apparatuses proposed in the related art that adopt a dual gas supply system whereby a plurality of different types of processing gases are supplied through two gas supply mechanisms (e.g., gas shower heads) separately disposed at an upper level and a lower level inside the processing container. In such a plasma processing apparatus, the upper-level gas shower is positioned above the lower-level gas shower head, and injects a non-depository gas such as argon.
The lower-level gas shower head is positioned above and parallel to the substrate, and injects a processing gas such as silane gas. With the different types of gases injected at specific positions within the processing container as described above, plasma is generated as desired and desirable plasma processing is executed on the substrate with the plasma thus generated.
However, the structure with the lower-level gas shower head disposed parallel to the substrate poses a problem in that great quantities of ions and electrons contained in the plasma collide with the lower-level gas shower head, which leads to overheating of the lower-level gas shower head and results in reaction product becoming settled on the lower-level gas shower head in large quantity. Consequently, the pile of deposit accumulating at the lower-level gas shower head becomes thicker than a certain level, peels off the lower-level gas shower head and settles onto the substrate as particles in a relatively short period of time.
The lower-level gas shower head having become heated during the processing operation is then cooled while the substrate is transferred into/out of a load lock chamber. Since the lower-level gas shower head is constituted of a dielectric member, it does not transfer heat readily. This means that the heat applied to the lower-level gas shower head as ions and electrons collide with the lower-level gas shower head is not readily transmitted to the outside. Thus, if ions and electrons collide with the lower-level gas shower head in great quantities, the lower-level gas shower head becomes overheated during the processing operation and then becomes rapidly cooled during the transfer operation. As the lower-level gas shower head is repeatedly heated and cooled, as described above, the temperature at the lower-level gas shower head undergoes drastic fluctuations.
Under such circumstances, the difference between the thermal expansion coefficient of the deposit (reaction product) and the thermal expansion coefficient of the lower-level gas shower head becomes a more significant factor to allow the deposit to peel off the lower-level gas shower head more readily. This, in turn, further reduces the length of time to elapse before the deposit settles onto the substrate as particles. This issue of particles settling on the substrate may be addressed by cleaning the inside of the processing container in shorter cycles. However, this solution leads to another problem in that the throughput is adversely affected to lower the productivity.
There is another problem in that if the flow of plasma being diffused toward the substrate is blocked by the lower-level gas shower head and great quantities of ions and electrons collide with the lower-level gas shower head, a significant extent of energy loss due to the collisions occurs, to result in plasma decay, which in turn, lowers the reaction velocity (e.g., deposition rate) at the substrate.
The present invention addresses the problems discussed above by providing a plasma processing apparatus that includes a gas injection member disposed at a position where the gas injection member does not block the flow of plasma onto a workpiece and a plasma processing method that may be adopted in the plasma processing.